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Monitoring Well Installation Report-Tosco(Former BP)S5#11195,Lathrop California rssr= July 24,2002 Approximately 61,000 gallons of groundwater were removed from the former and present UST pits during the 1998 construction activities, stored on-site in portable tanks, then transported by Waste Management Industrial Services (WMIS) of Benicia, California, to the Tosca Refinery in Rodeo, California, for treatment and disposal. Prior to backfilling and compacting of the former gasoline UST complex excavation, one conductor casing was placed near the northwest corner of the former UST excavation. The casing was installed to facilitate the removal of groundwater from within the former UST cavity. The conductor casing consisted of 11.5 feet of 6-inch diameter polyvinyl chloride (PVC) and 10 horizontal feet of 6-inch PVC in an "L"configuration extending eastward from the vertical section. The bottom 10 feet of the vertical casing and the horizontal casing consist of 0.02-inch machine slotted well screen. The location of the conductor casing is shown on Figure 2. Between February 26 and March 26, 1999, approximately 41,760 gallons of groundwater were removed from the former UST backfill utilizing the conductor casing. Groundwater removal and transportation was performed by WMIS. The water. was transported to the Tosco Refinery for treatment and disposal. A total of approximately 102,760 gallons of groundwater were removed from the former and present UST pits and transported to the Tosco Refinery between January 1999 and March 26, 1999. In February 2002, GR advanced five off-site geoprobe soil borings (B-I through B-5) downgradient of the subject site: Soil and groundwater samples were collected at each of the geoprobe locations and analyzed for TPHg (by EPA Method 8015 modified), and benzene, toluene, ethylbenzene, and xylenes (BTEX) and MtBE by EPA Method 8021. In addition;all soil and groundwater samples were analyzed for Ethanol, TBA, MtBE, di-isopropyl ether (DIPE), ethyl tert-butyl ether (ETRE), 1,2-dichloroethane (1,2 DCA), TAME, and ethylene dibromide (EDB) by EPA Method 8260B. None of the hydrocarbon constituents were detected in soil. Four groundwater samples (B-1,B-2, B-4, and B-5) contained MtBE at concentrations ranging from 3.0 to 10, 000 ppb. 3.0 FIELDWORK -In order to further evaluate groundwater conditions downgradient.of the site, GR installed five groundwater monitoring wells. Field work was conducted inaccordance with GR's Field Methods and Procedures (Appendix A), and the Site Safety Plan dated May 6, 2002. The monitoring wells ---were installedunderdrilling permit numbers 0029821 and 0029822, issued on May 16, 2002 by SJCPHS-EHD. Copies of the drilling permits are included in Appendix B. Underground Service Alert (USA) was notified at least 48 hours prior to drilling at the site (confirmatiol-#240951). As a precautionary measure, a private subsurface utility locator was contracted to identify utilities near the proposed boring locations. The borings were hand excavated for the first five feet bgs to further insure that no utilities were disturbed. 140193.12-2 4